Helping to bring a new generation of reactors to life

March 13, 2020, 9:13AMNuclear NewsJoel Hiller

As the nuclear industry pursues a new generation of reactors to meet economic and political realities, the process for developing and qualifying new fuels and materials has come into focus. It’s clear that the 30-year development process the industry has come to expect is no longer viable, just as the economic reality of the current reactor fleet is increasingly coming under pressure from low-cost alternatives, particularly natural gas. To reduce carbon emissions while meeting ever-growing energy needs, new nuclear plants must be built soon.

The current development cycle for nuclear materials. Image: DOE/INL

The industry is rising to that challenge, with a wave of innovative startups working on new reactor concepts that will power a smarter electrical grid. To maintain that momentum and interest, the Department of Energy’s Office of Nuclear Energy (DOE-NE) has created the new Nuclear Materials Discovery and Qualification Initiative (NMDQi). Headquartered at Idaho National Laboratory, NMDQi’s goal is to accelerate the discovery and qualification of new materials for advanced nuclear reactor designs to meet the needs of a revitalized nuclear industry, bringing materials to market much more quickly and at a lower cost. NMDQi takes a grand challenge approach to reducing the qualification process to approximately 10 years, rather than 20 to 30, while maintaining the same degree of safety and regulatory compliance that exists today.

A working meeting to engage the nuclear community was held at INL on October 17 and 18, 2019, with input from several organizations, including national laboratories and universities, as well as centers and commercial organizations focused on accelerated materials development. This input has been used to shape the vision for the initiative and guide collaboration as the NMDQi launches in 2020.

“We understand the daunting task of meeting regulatory qualifications in a manner that is both cost-effective and thorough,” said Allen Roach, director of NMDQi. “The innovation is happening already; we just need to help move things forward by creating the tools and capabilities to facilitate the process.”

Using multiscale modeling to predict material degradation in harsh environments. Image: DOE/INL

To achieve the lofty goal of reducing the qualification period by up to 67 percent, NMDQi has adopted the Materials Genome Initiative (MGI) approach to development. Initiated by the National Institute of Standards and Technology in 2011, MGI is a multi-agency initiative intended to accelerate the development process for industrial manufacturing. It relies on centralized data libraries to promote collaboration, as well as advanced computing tools and innovative fabrication techniques to model, refine, and scale-up new materials.

Adapting this process to incorporate the additional safety requirements needed for nuclear research on advanced reactors, NMDQi is focused on three key areas where progress must be made for new commercial reactors to be built:

Reactor pressure vessel steels:A variety of changes may take place in the microstructure of materials used in the reactor pressure vessel through prolonged exposure to irradiation. Voids and dislocations can form, trace elements and alloying might begin to separate, and precipitate formation may also take place. These changes result in embrittlement and other mechanical liabilities. NMDQi is taking advantage of decades of existing data regarding the longevity of RPVs and feeding the data into advanced models to create predictions that can speed the qualification of new materials.

Claddings:Cladding alloys made from zirconium have performed well in the current fleet of reactors, but they are not particularly well suited to the advanced reactor concepts currently under consideration. With a particular emphasis on safety, cladding for advanced fuels may need to withstand temperatures of 1,000°C while exhibiting sufficient physical and chemical stability. These alloys, including high-temperature ferritic steels and multiple principal element alloys, are currently being researched, but with over a billion potential alloys to consider, an advanced research framework is needed to identify and evaluate the most promising candidates.

Fuels:Naturally, one of the primary concerns for advanced reactor development is the fuel. The fuel for the next generation of reactors must display a high degree of accident tolerance while meeting other performance standards, such as neutron transparency, management of fission products, and cladding and coolant compatibility. Promising candidates include variations of metallic and molten salt fuels, as well as tristructural-isotropic (TRISO) fuel, all of which are currently undergoing high-throughput testing.

The NMDQi development process

NMDQi is moving forward to create a streamlined pathway to qualification of new materials. Researchers are focusing on four pillars to prioritize safety while reducing unnecessary delays.

1. Modeling and simulation: Physics-based modeling has become an indispensable part of the manufacturing process for advanced materials in every industry. For nuclear materials, the data needed to understand process-structure-property performance relationships include the behavior of materials in conditions that include irradiation, high temperature, and high pressure, all over an extended period of time. With access to new modeling tools that are continually being refined, researchers will be able to simulate years of wear and tear on a wide variety of fuel and reactor materials in a matter of weeks or months. Advanced modeling can help minimize the setbacks of real-world testing that invalidates a promising new alloy.

2. Fabrication: Utilizing the data from the modeling process, NMDQi next focuses on manufacturing several test specimens that exhibit different properties of interest. Multiple samples can then be examined in a single test. This provides a significant advantage over a more iterative, traditional approach to fabrication. The process is aided by advanced manufacturing techniques such as additive manufacturing as an alternative fabrication technique (AMAFT).

Isabella van Rooyen is the national technical director of advanced methods of manufacturing for DOE-NE and a distinguished staff scientist at INL. She was approached by Westinghouse Nuclear with the challenge of developing a new, more efficient method of producing uranium silicide (U3Si2) fuel, which displays desirable properties, including high thermal conductivity and a high melting point for accident tolerance. To streamline the process, she turned to additive manufacturing and developed AMAFT. This process is a form of 3-D printing that begins with uranium in a powdered form. Along with reactants, it is placed in a pressure vessel where it undergoes a series of heat reactions with the aid of a specialized laser. The reactions must take place in a precise order, with the temperature and pressure in the unit tightly controlled to create a fuel pellet with the correct density and makeup.

Using AMAFT to fabricate U3Si2 pellets offers three distinct advantages over other manufacturing processes:

Efficiency:The AMAFT process allows manufacturers to use products earlier in the supply chain to manufacture fuel. The fabrication can also be completed in a single, integrated unit. Other fuel manufacturing methods require a lengthy process of melting, grinding, and sintering that adds significant time and cost. The additive nature of the AMAFT process also leads to less wasted material.

Flexibility: Crucially, AMAFT can be used to manufacture U3Si2 fuel from UF6, UF4, U3O8, or uranium metal. This allows facilities to utilize uranium supplies already at hand for quicker, less expensive production. Based on the reactant used, a variety of desirable secondary products can also be formed during the process, which can be sold to recover a portion of the manufacturing cost.

Security: Because conventional fuel manufacturing requires so many steps using different tools, there is always the risk of material being stolen or misplaced. The simpler, self-contained AMAFT manufacturing unit is easier to keep secure.

Van Rooyen’s team is building the safety case for the use of AMAFT in production. The proof of concept has been demonstrated at INL with surrogate materials, including hafnium and cerium, with additional tests being planned in the fall. Van Rooyen stresses the potential of AMAFT to provide NMDQi with a significant advantage as it seeks to streamline fuels qualification. “We’re looking at a 20 percent reduction in cost and time,” van Rooyen said. “Because we need to look at cost efficiency and time savings every step of the way, AMAFT is integral to helping the industry achieve its goal to build new, advanced reactors.”

Representation of the multiscale modeling approach for fuel performance, using the MOOSE simulation framework. Image: DOE/INL

3. Testing:While streamlining the materials manufacturing process helps reduce the time needed to qualify new fuels and materials, the testing phase is vital to ensuring that the materials will hold up in real-world reactor conditions. NMDQi uses two different high-throughput reactors at INL to assess the performance of fuels and materials before relying on them in an operating reactor.

The Advanced Test Reactor (ATR) provides researchers with steady state testing and a high rate of neutron flux, so years of operational wear can be achieved in a matter of months. ATR’s unique design allows multiple experiments to be performed simultaneously with varying neutron flux, allowing researchers to shorten overall test times for new fuels, cladding, or other reactor materials.

The Transient Reactor Test Facility (TREAT) helps researchers understand how new fuels and materials perform in off-normal operational circumstances. With safety being the top concern for any new reactor technology, it’s vital to determine how new fuels, cladding, and containment materials handle rapid power fluctuations. U3Si2 fuel pellets, for example, have been tested in TREAT. The necessary information was collected approximately three transients ahead of schedule. This vital testing capability can save years in the qualification process for the next generation of reactors while ensuring that the highest safety standards are met.

4. Data analysis: NMDQi’s data analytics focuses on overcoming the relative lack of information on new materials by feeding the existing data to machine and deep learning algorithms that are informed by the latest physics-based modeling, supplemented with new experimental data as it is collected. It aims to establish a common framework for data collection throughout the industry. As more information is collected and shared between organizations, researchers can make updates to models and designs to create effective behavioral predictions, quickly progressing toward viable end products.

Collaboration

The key to achieving NMDQi’s objectives is effective collaboration throughout the nuclear community. With multiple national laboratories, universities, and private companies working to overcome technical and regulatory hurdles, sharing the load brings a faster resolution to challenges. NMDQi is currently forming partnerships with a wide variety of organizations, with the aim of sharing resources and building on each other’s progress rather than competing against it. The resulting collaborative environment means that progress is achieved more quickly, and each organization has access to a much wider talent pool than it would have alone. NMDQi is in the early stages of developing partnerships, and in the coming months, it is anticipated that groups will begin populating the common data collection framework and sharing expertise.

Building a new generation of nuclear reactors is a tremendous undertaking. From the earliest conceptual stages through regulatory approval and eventual construction, it is time-intensive and costly. The need for abundant clean power, however, has never been greater, and increasing the availability of nuclear energy represents the most feasible path to meet baseload power requirements as renewable technologies continue to mature. NMDQi represents a nationwide effort to streamline the lengthy development and qualification process for new nuclear fuels and materials by leveraging advanced modeling, fabrication, testing, and data management techniques in a collaborative network of research organizations.

“There’s still so much potential development in nuclear power,” said Steven Hayes, director of the Fuels and Materials Division for the Nuclear Science and Technology Directorate at INL. “It’s exciting to be a part of this new era of innovation that can help us meet our growing energy needs while reducing carbon emissions.”


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